This invention relates to the recovery of base metals from tailings and is more particularly concerned with the oxidation of sulphide minerals in tailings dams or dumps.
A substantial amount of literature exists relating to the heap leaching of waste rock by natural oxidation through bacterial action. Oxidation of this type requires that air can freely penetrate the rock. This is usually the case for the rock is relatively coarse and the air can easily penetrate into the interior of a pile of rock. The bacteria are then capable of oxidising the sulphide minerals and the base metals may be dissolved by solution percolation through a rock pile.
If a tailings dump is formed from material with a fine particle size, for example with a particle size which is less than 100 microns, then the dump is normally naturally compacted and the ability of air to penetrate to the interior of the dump is at best restricted but more generally prevented.
Two publications have addressed the problem of bacterial leaching of tailings with fine particle size, i.e. slime, for the recovery of gold. Reference is made in this regard to:    1. Livesey-Goldblatt E. Bacterial leaching of gold, uranium, pyrite bearing compacted mine tailing slime. In: Lawrence R W, Branion R M R, Ebner G H, eds. Fundamental and Applied Biohydrometallurgy. New York: Elsevier, 1986:89–96;    2. Lawson E N, Taylor J L, Hulse G A. Biological pre-treatment for the recovery of gold from slime dams. Journal of South African Institute of Mining and Metallurgy, 1990;In the processes described in the these publications oxidised minerals in the form of soluble iron and sulphate are dissolved. These processes are not however directed to the recovery of base metals.